The subject matter disclosed herein relates generally to systems and methods for computed tomography (CT) imaging, for example to systems and methods for reducing periodic artifacts in CT images.
In CT imaging, an X-ray source may be rotated around an object to obtain imaging information. X-rays from the source attenuated by the object may be collected or detected by a detector and used to reconstruct an image.
In modern CT imaging, there are a number of non-ideal physical conditions that may cause artifacts in reconstructed CT images. For example, one such condition is off-focal radiation or extra-focal radiation. Off-focal radiation is caused mainly by two effects: secondary electrons and field emission electrons. The secondary electrons are typically the more dominant source. For example, when a high-speed electron beam strikes a target, electrons are again emitted from the impact area. Most of these high-velocity secondary electrons (backscatter electrons) return to the target at points outside the focal spot and produce x-ray photons at their point of impact.
Off-focal radiation may cause various problems in medical CT imaging. For example, off-focal radiation increases radiation dose to a patient. As another example, off-focal radiation may create image artifacts due to data inconsistency induced by the erroneously elevated photon counts at the detector. The impact of off-focal radiation may be dependent on the location of an object being imaged (or portion thereof) relative to the iso-ray as well as the distance to the x-ray focal spot. When off-focal radiation is present after data calibrations and data corrections, shading and blooming artifacts may appear in reconstructed images.